Conventional X-ray imaging provides image contrast based on absorption and often provides low contrast for biological specimens. Phase contrast X-ray imaging can provide superior contrast, diffraction enhanced images have been obtained using Bragg analyzer crystals and free space propagation of transversely coherent waves. X-ray differential phase contrast (DPC) imaging using a Talbot grating interferometer has been demonstrated. Quantitative phase retrieval by a phase stepping method has also been demonstrated. Unfortunately, phase stepping is a mechanical process in which one grating is physically moved in multiple steps over a grating period in order to obtain a single differential phase image. Accurate mechanical movement of centimeter-size objects such as X-ray gratings at a sub-micron level is inherently slow, and difficult to reproduce precisely without a static and stabilized platform. In common configurations including fluoroscopes and CT scanners, precision motors must be mounted on moving gantries, leading to additional mechanical instability. X-ray phase imaging methods and apparatus that do not require difficult to realize mechanical movements are needed.
Scattering of X-rays by the material of a specimen creates a diffuse background in the images which degrades the quality of radiography and CT images. Absorption grids are placed in the beam to either physically block the scattered X-rays, or provide a scatter-corrected image based on demodulating the projected grid pattern in the image. In this case, the grids must be mechanically moved in order to remove the grid pattern in the final images. This mechanical movement is inherently slow, and mechanical actuators add cost and require maintenance. Methods that do not require mechanical movements also benefit these applications.